14

Qt documentation about QTime::currentTime() says :

Note that the accuracy depends on the accuracy of the underlying operating system; not all systems provide 1-millisecond accuracy.

But is there any way to get this time with milliseconds accuracy in windows 7?

HMD
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  • Is this what you are looking for? http://stackoverflow.com/questions/3729169/how-can-i-get-the-windows-system-time-with-millisecond-resolution – Donald Jul 30 '15 at 20:03

4 Answers4

15

You can use QDateTime class and convert the current time with the appropriate format:

QDateTime::currentDateTime().toString("yyyy/MM/dd hh:mm:ss,zzz")

where 'z' corresponds to miliseconds accuracy.

Sid Mhatre
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Ritchy MFinda
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3

you can use the functionality provided by time.h header file in C/C++. 

#include <time.h> 
clock_t start, end; 
double cpu_time_used; 
int main()
{
    start = clock();
    /* Do the work. */ 
    end = clock(); 
    cpu_time_used = ((double)(end-start)/ CLOCKS_PER_SEC);
}
Anurag Singh
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2

Timer resolution may vary on different platforms and readings may not be accurate. If you need to get high-resolution, accurate timestamps on Windows 7, it provides QPC API:

https://msdn.microsoft.com/en-us/library/windows/desktop/dn553408%28v=vs.85%29.aspx

GetSystemTimePreciseAsFileTime is claimed to provide system time with <1us resolution.

But that's only about accurate timestamp. If you need to actually do something with 1 ms latency (ex. handle an event), you need a RTOS, not a desktop clunker.

ezaquarii
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0

One common way would be to scale up whatever you are doing and do it 10-100 times in a row, that way you would be able get a more accurate time reading of whatever you are doing, by dividing the result by 10-100.

But getting millisecond precise readings of your time is pretty much useless because you don't have 100% of the cpu time, which means that your readings will have much greater variance than just 1 millisecond if the OS gives another process computing time while you are doing your actions.

  • thank for your response but It's not a synchronous operation and I need to calculate 1-milliseconds accurate between my data and I don't think milliseconds time accuracy need to have 100% of CPU's time. there must be a way. – HMD Jul 30 '15 at 20:13
  • @ATN Just remember that the delay between the data arriving and your process being notified of its arrival will be random and can be on the order of hundreds of milliseconds in bad cases. Whatever timing data you get must be processed statistically, using an appropriate error model. – Kuba hasn't forgotten Monica Jul 31 '15 at 12:37